The present invention relates to a process for producing 2,2'-bis(hydroxymethyl)alkanoic acid, and more particularly to, an industrially useful process for producing 2,2'-bis(hydroxymethyl)alkanoic acid, which process includes an improved step for recovery of the alkanoic acid. The 2,2'-bis(hydroxymethyl)alkanoic acid (hereinafter referred to merely as "dimethylol alkanoic acid") can be produced by the oxidation of 2,2'-bis(hydroxymethyl)alkanal (hereinafter referred to merely as "dimethylol alkanal"), and is useful as a raw material for the production of polyesters, polyurethanes, alkyd resins or the like.
The dimethylol alkanal can be obtained by condensation-reacting aliphatic aldehyde having two hydrogen atoms bonded to .alpha.-carbon atom thereof, with an appropriate amount of formaldehyde in the presence of a base (refer to the following reaction formula (I)). Upon the condensation reaction, 2-substituted acrolein is by-produced. Alternatively, the dimethylol alkanoic acid can be produced by the oxidation of dimethylol alkanal (refer to the following reaction formula (II)). The by-produced 2-substituted acrolein is converted into dimethylol alkanal by reacting with an appropriate amount of formaldehyde in the presence of a base (refer to the following reaction formula (III)). ##STR1##
As the bases (condensation catalysts) used in the production of dimethylol alkanal, there have been proposed sodium hydroxide (Japanese Patent Publication (KOKOKU) No. 52-20965(1977) and Japanese Patent Application Laid-open (KOKAI) No. 62-263141(1987)), sodium carbonate (U.S. Pat. No. 3,312,736), triethylamine (Japanese Patent Publication (KOKOKU) No. 4-55181(1992)), dimethylamino neopentanol (German Patent No. 2,507,461) or the like.
Specifically, for example, in U.S. Pat. No. 3,312,736, there is described a process in successive steps from the production of dimethylol alkanal to the recovery of dimethylol alkanoic acid, comprising reacting n-butyl aldehyde with formaldehyde in a water solvent in the presence of sodium carbonate, treating the reaction solution with hydrogen peroxide, removing inorganic substances derived from sodium carbonate, from the reaction solution using sulfonate-type cation exchange resin, subjecting the reaction solution to evaporation treatment, and cooling and then filtering the reaction solution to obtain 2,2'-bis(hydroxymethyl)butanoic acid as a solid.
However, in the above-mentioned conventional process, a large amount of wash water is required to regenerate the cation exchange resin, so that a large amount of waste water must be treated subsequently, which is extremely disadvantageous from the industrial viewpoint.
As a result of the present inventors' studies, it has been found that in an alkanoic acid recovery step, by adding a mineral acid to an aqueous solution containing the 2,2'-bis(hydroxymethyl)alkanoic acid and the base, in an amount of not more than one equivalent based on the base in the aqueous solution to convert the base into a salt thereof; adding an organic solvent to the aqueous solution to replace water in the aqueous solution with an organic solvent, thereby forming an organic solvent solution; and after removing the mineral acid salt precipitated from the obtained organic solvent solution, crystallizing 2,2'-bis(hydroxymethyl)alkanoic acid from the organic solvent solution, 2,2'-bis(hydroxymethyl)alkanoic acid can be recovered in a high yield. The present invention has been attained in the basis of the finding.